Synthetic grease compositions

ABSTRACT

NOVEL HIGH TEMPERATURE SYNTHETIC GREASE COMPOSITIONS COMPRISE A SLECTED ESTER REFINED WITH A GLYCIDYL ESTER OF AN ALIPHATIC ACID CONTAINING FROM 5 TO 22 CARBON ATOMS AND A METALLIC SOAP.

United States Patent O M 3,585,138 SYNTHETIC GREASE COMPOSITIONS Raymond H. Boehringer and Robert E. Vail, Cincinnati, Ohio, assignors to Emery Industries, Inc., Cincinnati, Ohio N Drawing. Filed Oct. 13, 1969, Ser. No. 866,000

Int. Cl. C10m 5/14 US. Cl. 252--37 6 Claims ABSTRACT OF THE DISCLOSURE Novel high temperature synthetic grease compositions comprise a selected ester refined with a glycidyl ester of an aliphatic acid containing from 5 to 22 carbon atoms and a metallic soap.

BACKGROUND OF INVENTION (1) Field of invention This invention relates to synthetic grease compositions, and more particularly to compositions containing a selected ester refined with a glycidyl ester and a metallic soap.

(2) Prior art Metallic soap greases have been made containing low molecular weight aliphatic esters. However, while these esters are acceptable for low temperature grease applications, they are too volatile at high temperatures (400 F. and higher). In general, complex and polyol esters are unsatisfactory because they contain an excessive amount of acidity in the form of unreacted acids used in the preparation of the ester. The presence of these unreacted acids prevents the formation of satisfactory grease consistency when the ester is combined with a metallic soap. The excess acidity is present because of the nature of the ester condensation reaction.

A number of methods have been attempted in the past toreduce the acidity of the esters used for base fluids in metallic soap greases. One of the most common methods 3,585,138 Patented June 15, 1971 free acidity of organic ester materials. The primary problem with epoxidized oils has been that they are not capable of reducing the acidity to the low level required in order that the ester will form a grease when compounded with a metallic soap.

The esters that are used as base fluids for high temperature synthetic greases must have an acid value of no more than 0.1 and preferably 0.05 or lower in order to form a satisfactory grease when combined with a metallic soap. It has now been found that treatment of selected esters with a glycidyl ester of an aliphatic acid, in accordance with the process described in US. application Ser. No. 650,185 filed June 30, 1967, now US. Pat. 3,485,754 dated Dec. 22, 1969, produces synthetic base fluids for greases which have exceptionally low acid values, e.g., as low as 0.01.

SUMMARY OF INVENTION This invention relates to synthetic grease compositions comprising a selected ester refined with a glycidyl ester of an aliphatic acid containing from 5 to 22 carbon atoms and a metallic soap.

DESCRIPTION OF INVENTION Esters which may be utilized in the present invention a may be prepared from polyols, particularly those polyols has been the treatment of the acid-alcohol reaction product with an aqueous alkali solution such as potassium carbonate or sodium hydroxide or the percolating of the ester reaction product through an alkaline bed. While being effective in reducing the acid value in some esters, the;alkali treatment has not been satisfactory for the esters required in high temperature greases. Due to the high molecular weight of these esters, attempts to water-wash the esters to remove the soaps formed by alkali refining result in either (1) emulsions which are diflicult or impossible to break and a corresponding loss of ester, or (2) the mixture fails to separate because the soap is more soluble in the ester layer.

Another method which has been used for the removal of excess acidity from the higher molecular weight esters has been the treatment of the unrefined ester with shortchain alkylene oxides, such as propylene oxide or ethylene oxide. One of the drawbacks to this latter mentioned process is that the reaction products of the alkylene oxides, particularly the lower alkylene oxides, and the free acid is a material which is generally unstable under the high temperature operating conditions to which the synthetic lubricant greases are subjected, and accordingly, either decompose, resulting in the contamination of the lubricant grease or produce a grease with excessive volatility. Another problem connected with the use of alkylene oxides is their tendency to polymerize causing the introduction into the ester of undesirable polymeric materials which are difficult to remove.

Epoxidized oils, in which the epoxy group is contained in an internal position, have also been used to reduce the with a neo-pentyl group, and monocarboxylic acids having from about 10 to about 22 carbon atoms. Suitable polyols include neo-pentyl glycol, trimethylolpropane, pentaerythritol, diethylene glycol, trimethylolethane and mixtures thereof. Other esters may also be prepared from polycarboxylic acids having from about 12 to 54 carbon atoms such as dimer and trimer acids and monohydric aliphatic alcohols having from about 6 to 20 carbon atoms.

Examples of the above esters are pentaerythritoltetraisostearate, pentaerythritoltetrapelargonate, di-(2 ethyl hexyl) dimerate, and tri-(Z-ethylhexyl) trimerate, etc. Complex esters suitable for use in the present invention may have a structural formula such as: X-YZYX, wherein X is a monohydric alcohol residue, Y is a dibasic acid residue, and Z is a polyol residue, or a structural formula such as ABCBA, wherein A is a monocarboxylic acid residue, B is a polyol residue, and C is a dicarboxylic acid residue. Examples of complex esters which may be treated by the process of this invention are the reaction products of sebacic acid, trimethylpropane, and pelargonic acid; sebacic acid, 1,3,4,7-octanetetrol and pentanoic acid; and ethylene glycol, 1,4-butanediol, adipic acid and azelaic acid.

Prior to the present invention the foregoing esters were not suitable for this use because (1) the excess acidity resulting from the free acid present prevented the ester from thickening to a satisfactory grease consistency when compounded with a metallic soap thickener, and (2) the standard methods for refining either left soap in the ester or to much ester was lost in the process of removing the soap.

The selected ester base fluids are refined in accordance with the method of U.S. 3,470,619. In general, the process is performed by introducing into the unrefined ester sys tern a sufficient amount of a glycidyl ester to react with the entire residual acid content of the unrefined ester. The glycidyl esters react with the free acids in the ester to form a hydroxy ester compound with the basic reaction being as follows:

wherein R is a branched or straight chain alkyl group having from about 4 to 21 carbon atoms, preferably having a neo structure and from about 7 to 9 carbon atoms, and R is the residue of a monocarboxylic acid, a dicarboxylic acid, a half ester of a monohydric alcohol, a

' dicarboxylic acid or carboxyl terminated polyester.

In carrying out the process, the acid value of the unrefined ester is determined and then at least a stoichiometric amount of glycidyl ester is added, but preferably an excess of from about 5 to 100 equivalent percent over the stoichiometric amount required for reaction with all of the carboxyl groups. The reaction may be carried out over a wide temperature range of about 150 to 250 C. and preferably 210 to 230 C. The time of the reaction is dependent upon the temperature used and the amount of the free acid which is present. Normally, at a temperature of about 220 C. the reaction may be carried out for a period of from about two to four hours. After the desired level of acid scavenging is completed, the excess glycidyl ester remaining in the ester may be stripped from the product at a temperature of about 250 C. and at a pressure of from about 1 to 5 torr.

The glycidyl esters which may be used as acid scavengers in the present invention include the glycidyl esters of aliphatic acids having from 5 to 22 carbon atoms. The acids may be the normal isomers although it is preferable that they be branched and more preferably that they be neo-acids. That is, acids in which the alpha carbon atoms are completely substituted with alkyl groups are most preferred. The glycidyl esters useful in the present invention are formed by the reaction of epichlorohydrin and an alkali metal salt of the acid of the type described above and should have the general formula:

ll RCCHz-CHOH wherein R is a branched or straight chain alkyl group having from 4 to 21 carbon atoms. The preferred acid scavenging glycidyl ester is a compound having the genwherein R R and R are all saturated alkyl groups and contain a total of from about 7 to about 9 carbon atoms. The glycidyl esters having this structure produce, when reacted with the free acid of the ester, materials which are particularly stable and compatible with metallic soap synthetic lubricant grease system. Consequently, expensive and difiicult removal steps need not be attempted prior to preparation of the grease composition. Among other glycidyl esters which may be used in the present invention, in addition to the neo-acid esters are the glycidyl esters of pelargonic acid, heptanoic acid, valeric acid, isostearic acid, and oleic acid.

The soaps used to thicken the base fluid ester to form the grease may be prepared from fatty acids having from 10 to about 22 carbon atoms such as lauric, palmitic, stearic and oleic acids. The preferred acids are saturated fatty acids such as stearic and l2-hydroxystearic acids. Suitable metals include those metals found in groups lzz, 2a, 4a, and 2b of the Periodic Table. While metals such as aluminum, zinc and magnesium may be used to prepare the soaps, the preferred soaps are made from the fatty acids with alkali and alkaline earth metals such as lithium, sodium, potassium, calcium, barium, and strontium.

The soap and desired stabilizers or additives are added to the base fluid ester and heated to a temperature of 190 to 210 C. until the mixture becomes clear. The mixture is then rapidly cooled and homogenized. In general, the base fiuid ester, or mixtures thereof, may constitute from 70 to 95 percent by weight of the mixture and preferably 88 to 95 by weight. The soap may constitute from to 25 percent by weight of the mixture and preferably 7 to 11 percent by weight. In addition, additives and stabilizers may constitute from 0.5 to 5.0 percent by weight of the mixture.

These additives and stabilizers may include, but are not limited to, diphenyl amine, zinc naphthenate, dinaphthyl amine, ditolyl amine, tricresylphosphate, sorbitan mono oleate, and phenothiazine. Suitable antioxidant additives are described in US. 3,247,111. A particularly effective high temperature grease consists of 89.5 percent pentaerythritoltetraisostearate, 8.0 percent lithium 12-hydroxy stearate, 2.0 percent sorbitan mono oleate and 0.5 percent purified phenothiazine.

The hydroxy ester products formed in reducing the excess acid components are fully compatible in the synthetic grease system and possess excellent high temperature qualities, and accordingly, do not detract from the lubricity of the grease. In fact, they supplement the lubricity while alleviating, because of stability, the usual need for removal of the free acid reaction product.

Following the method described herein, it has been possible to lower the acid value of those esters suitable for high temperature synthetic greases to the point that no carboxyl content is detectable. This process not only makes available certain esters for synthetic lubricant greases that were not heretofore practical to use, but it also makes it possible to refine the ester in the same vessel in which it is prepared in the initial esterification reaction alleviating the need for additional handling and equipment. This is possible because of the relatively short time which is required to accomplish the reduction of the acid value to the desired level and the simplicity of the process.

To further illustrate the method of the present invention, the following examples are provided. It is to be understood that these examples are illustrative only and are not to be considered limitations on the scope of the invention.

EXAMPLE 1 3500 grams of an ester, tri-(2-ethylhexyl) trimerate, the reaction product of 2-ethy1hexyl alcohol and trimeric acid (a tribasic polymerized oleic acid having about 54 carbon atoms), was prepared. The acid value of the tri-(Z-ethylhexyl) trimerate was determined to be 2.8. A reaction vessel containing the tri-(2-ethylhexyl) trimerate was charged with 85.5 grams of the glycidyl ester of a neo-acid (sold under the trade name CARDURA E), having a molecular weight average of 245. The 85.5 grams represented a percent excess over the stoichiometric amount required to react with all of the free acid contained in the ester. The reaction vessel was heated to a temperature of 220 to 230 C. for three hours after which the excess glycidyl ester was stripped off at a temperature of about 245 C. and a pressure of 2 to 3 torr. The resultant ester had an acid value of 0.05.

EXAMPLE 2 1800 grams of an ester, pentaerythritoltetraisostearate, was prepared by the esterification of pentaerythritol with isostearic acid. The acid value of the ester was determined to be 3.50. The unrefined ester was divided into three portions, A, B, and C.

The first portion was retained as an unrefined ester to be compounded with a metallic soap. The second portion B, was refined as described in Example 1, with a resulting acid value of 0.05. This portion was also retained to be compounded with a metallic soap.

The third portion, C, was refined with sodium hydroxide by the following procedure. The unrefined ester was first diluted with an equal volume of toluene, then sodium hydroxide in an amount of about 300 percent excess of the stoichiometric requirements for reaction with the free acid was added as a 10 percent aqueous solution. After vigorous agitation, the excess caustic solution, including the soap heel, was allowed to settle from the organic layer and drawn off. .The organic solution was then washed with Percent Ester 89.5 Lithium 12-hydroxystearate 8.0 Soribitan mono oleate 2.0 Purified phenothiazine 0.5

After heating the formulations to 200 C. and stirring until clear each was quickly cooled and homogenized.

The first grease using the unrefined ester did not have a good grease consistency and when tested by ASTM Designation D217-48 it had a penetration below the lower limit of the test (greater than 380 tenths of millimeters). The second and third greases has a good grease consistency and had a penetration of 245 and 255, respectively.

The above example shows that an ester refined with a glycidyl ester may be compounded into an excellent grease composition compound as compared with the unrefined ester compositions. This example also shows that the glycidyl ester refining produced a product equivalent to a sodium hydroxide refined product without the difficulty or loss of product that is attendant with caustic refining.

What is claimed is:

1. A high temperature synthetic grease composition comprising (A) from about 70 to 95 percent by weight of an ester lubricant base fluid which has been refined with a glycidyl ester of an aliphatic acid containing from about to 22 carbon atoms wherein the ester base fluid is selected from the group consisting of (a) an ester prepared by the reaction of a polyol, selected from the group consisting of neopentyl glycol, trimethylolpropane, pentaerythritol, diethy-lene glycol, trimethylolethane and mixtures thereof; with an aliphatic monocarboxylic acid containing from to 22 carbon atoms;

(b) an ester prepared by reacting a polycarboxylic acid selected from the group consisting of dibasic carboxylic acid having about 36 carbon atoms and tribasic carboxylic acid having about 54 carbon atoms produced by polymerization of aliphatic unsaturated monobasic acids of about 18 carbon atoms with a monohydric aliphatic alcohol containing from 6 to 20 carbon atoms;

(c) a complex ester of the formula X-YZ-Y--X wherein X is a monohydric alcohol residue, Y is a dibasic acid residue, and Z is a polyol residue; and

(d) a complex ester of the formula A-B-C-B-A wherein A is a monocarboxylic acid residue, B is a polyol residue, and C is a dicarboxylic acid residue and (B) from about 5 to 25 percent by weight of a metallic soap of a fatty acid containing from 10 to 24 carbon atoms wherein the metal is selected from the group consisting of the metals of groups 1a, 2a, 4a and 2b of the Periodic Table.

2. A synthetic grease as in claim 1 wherein the ester base fluid is present in an amount from about 88 to percent by Weight and the metallic soap is present in an amount of from 7 to 11 percent by Weight.

3. A composition as in claim 2 wherein said glycidyl ester is selected from the group consisting of glycidyl esters of aliphatic neo-acids having from about 4 to 21 carbon atoms, pelargonic acid, valeric acid, isostearic acid, heptanoic acid, and mixtures thereof.

4. A composition as in claim 3 wherein a major amount of the metal soap contains from 16 to 18 carbon atoms and the metal portion is selected from the group consisting of lithium, sodium, potassium, calcium, barium, and strontium.

5. A composition as in claim 4 wherein stabilizers and additives are present in an amount of from about 15 to 5 percent by weight.

6. A composition as in claim 5 wherein the metallic soap is selected from the group consisting of the metal soaps of stearic acid and 12-hydroxy stearic acid.

References Cited UNITED STATES PATENTS 2,448,567 9/1948 Zisman 25242 2,450,222 9/ 1948 Ashburn 252-42X 3,362,906 1/1968 Cyba 252-42X 3,485,754 12/1969 BOylan 252-56 DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner U.S. Cl. X.R. 25240.5, 41, 42 

